This invention relates to safety hatch cover apparatus, and more particularly to such apparatus permitting controlled venting of pressurized gas from a container closed by the hatch cover and having locking means which provide increased safety in locking the hatch cover in its closed position and unlocking it from its closed position.
The invention has particular application as hatch cover apparatus at the top of a tank of a highway tank truck or tank trailer vehicle adapted to contain vaporizable or flammable liquids such as gasoline. Therefore, the invention will be discussed below largely in connection with such use.
United States and state regulations require that the upper part of the tank of such a vehicle, such as a tank dome in which the hatch cover apparatus may be installed, be capable of adequately venting the tank to protect it from the effects of excessive superatmosphere and subatmospheric pressures. In conventional practice, the tank dome usually includes pressure vapor valve means which permits venting of gas from the tank or entrance of air into the tank. Generally, such a valve is designed so that if the tank overturns the valve shuts completely off. The tank dome also usually has a fusible plug to release gas or liquids from the tank in the event that the tank is exposed to excessive temperatures as from fire. Other valves may be provided for other purposes.
A hatch opening is provided, preferably in the dome, to allow access to the tank interior by personnel for inspection, cleaning or repair, or for use in filling the tank, and a hatch cover is provided to open and close the opening. Means are provided to lock the cover closed. It is necessary, however, even though the hatch cover be locked closed, if internal pressure exceeds a predetermined amount, that there be venting from the tank. It is also necessary that the hatch cover apparatus provide safety by preventing the hatch cover from opening due to vibration during travel of the vehicle carrying the tank, and also to provide safety for an operator in opening the hatch cover in the event of substantial gas pressure in the tank at the time of opening. It is also desirable that the hatch cover apparatus and its locking mechanism be of strong construction and simple in operation.
In general, prior apparatus has not provided all of these necessary or desirable features. U.S. Pat. No. 4,024,983 provides a hatch cover construction for a tank having locking means embodying on the cover a latch bar that is rotatable about an axis normal to the cover and that when in locking position has its ends engaged with keepers mounted on a base member connected to the tank dome and providing the hatch opening; the keepers are movable and spring loaded so they can move outwardly to allow the cover to rise to permit venting of excessive gas pressure. This patent discloses no safety features restraining inadvertent rotation of the latch bar to release the hatch cover. Its apparatus is susceptible to malfunctioning because its springs are exposed to the contents of the tank. In addition, the keepers are movable and guided by the shaft which is sealed with rubber O-rings, which could be a potential source of malfunctioning.
U.S. Pat. No. 2,093,694 discloses a hatch cover construction for a tank, having a latch bar rotatable about an axis normal to the cover and engaging keepers and having elements inside of the tank enclosure which are claimed to prevent inadvertent rotation of the latch bar. However, the structure is very different from that of the present invention. It is complicated, more expensive and more liable to get out of order, particularly because of exposure of most of the structure to the contents of the tank.
U.S. Pat. No. 3,744,670 discloses a different type of hatch cover construction not embodying a rotatable latch bar but, rather, transverse bars that hold the cover down and a spring-loaded arrangement operating between the cover and one of the transverse bars that urges the cover downwardly but allows it to rise to permit venting. The structure is very different from that of the present invention and considerably more complicated and expensive to manufacture; it also lacks the safety features of the invention.
It is an object of the invention to provide all or as many as desired of the desirable factors indicated above, and to overcome the deficiencies of the prior art.
It is a further object to provide safety features to prevent the hatch cover from unlocking during travel of the vehicle over the road, and to provide safety for the operator on the opening of the hatch cover in the event that there is substantial gas pressure in the tank.
In accordance with these objects, the invention provides hatch cover apparatus for a tank comprising a base member fixed to the tank and having an opening providing access to the tank; a pair of keeper members rigidly fixed to the base member at opposite sides of the opening, each keeper member providing lateral access for an end of a latch bar; a cover associated with the base member and adapted to be put in closed position to engage the base member and close the opening and to be put in opened position to open the opening; an elongated latch bar adapted to have its ends engaged with the keeper members when the cover is in its closed position and to be disengaged from the keeper members when the cover is in opened position; means on the cover for mounting the latch bar on the cover so that it has clearance in the direction perpendicular to the cover and is capable of limited twisting or transverse movement relative to the cover to engage and disengage the keeper members and of rotation about its longitudinal axis, said latch bar being thus rotatable in the plane of the cover between a position in which its ends are engaged with the keeper member and another position in which its ends are not so engaged; a cam adapted to be rotated about the longitudinal axis of the latch bar with projecting external surface portions that are located a maximum distance from the latch bar axis toward the cover when the cover is in its closed position and retracted external surface portion means located a lesser distance from said latch bar axis and away from the cover when said cover is not in its closed position; resilient biasing means operating by cooperation of the cover, the latch bar, the cam and the keeper to urge the cover toward the base when the cover is closed and the latch bar ends are engaged with the keepers, whereby gas pressure above a predetermined amount within the tank and urging outwardly on said cover against the biasing force of the biasing means will cause at least a portion of the cover to lift from the base and permit escape of gas from the tank; and, preferably, means cooperating between the latch bar mounting means and the latch bar and located outside of the containers to restrain the latch bar from moving from the position where its ends are engaged with the keeper means to a position where it might open.
According to another aspect of the invention, the means for restraining the latch bar also operates to restrain the latch bar from moving from its position where its ends are engaged with the keeper means even though the cam means is turned about the axis of said latch bar so that its projecting surface portion means does not engage said resiliently biased means.